Many types of so-called wireline service operations are performed in earth boreholes, particularly in the petroleum industry, in oilwell drilling and production operations. The broad class of wireline service operations with which the present invention is concerned is the one wherein the wireline comprises one or more insulated electrical conductors contained without an outer sheath and the wireline is utilized both to suspend a downhole tool in a borehole and to transmit electrical signals between the downhole tool and aboveground equipment. The term "wireline" as used herein always refers to the type wireline as just described and never to the solid type wireline commonly referred to in the industry as a "slick line".
The conventional wireline that has been used for many years in the industry and which is still the industry standard, has a sheath or armor make up of one or more layers of steel wires, the first layer consisting of steel wires laid side by side about the periphery of the inner conductor insulation and spirally wound thereon, with the next layer consisting of steel wires laid side by side about the periphery of the first layer and spirally wound thereon, etc.. A typical single conductor wireline may be United States Steel Type 1N12SV, Electromechanical Cable, which has an inner conductor of stranded copper wire covered by propylene polymeric material, commonly referred to as propylene copolymer insulating material, a first armor layer consisting of twelve wires and a second armor layer consisting of eighteen wires. This wireline has a nominal diameter of 1/8 inches.
This conventional type wireline is subject to severe disadvantages. There is considerable void space between the armor or sheath wires, so that corrosive borehole fluids can fill the voids and cause rapid deterioration of the expensive wireline. Of even greater significance are the problems encountered in trying to "pack off" the line as it enters the borehole so that internal pressures at the borehole surface are contained. Several methods have been devised for such "pack off" but none is entirely satisfactory. The pressure that the "pack off" or sealing element must exert on the wireline for a successful seal can cause the armor wires to part and "bird-cage" or to break and stack up below the "pack off".
The disadvantage of the conventional type wireline above mentioned have long been recognized. Further, it has been recognized, for a long time, that these disadvantages would be overcome by the provision of a wireline having a solid sheath presenting a smooth, closed exterior surface. The use of such a sheath to house electrical conductors in well survey apparatus is disclosed by Terwilliger, et al, in U.S. Pat. No. 3,443,429.
The prior art is replete with examples of electric cables wherein an insulated electrical conductor or conductors are contained within a smooth walled metal sheath, and the methods of making same. Such prior art is exemplified by U.S. Pat. Nos. 1,846,070, 2,105,168, 3,005,038, 3,356,790, 3,436,287, 3,480,724, 3,567,846 and 3,602,633.
There is, however, no prior art of which I am aware, that discloses, or teaches how to make, a wireline that comprises one or more insulated conductors contained within a smooth walled metal sheath and which wireline would be satisfactory to perform all of the normal wireline operations in a borehole and particularly in very deep boreholes.
It is, accordingly, the object of this invention to provide an improved wireline that comprises one or more insulated conductors contained within a smooth walled metal sheath which improved wireline would be satisfactory to perform all of the normal wireline operations in a borehole and particularly in very deep boreholes.
This and other objects are effected by the invention as will be apparent from the following description, taken in accordance with the accompanying drawings, forming a part of this application.